Various types of devices have been developed for implantation into the human body to provide various types of health-related therapies, diagnostics and/or monitoring. Examples of such devices, generally known as implantable medical devices (IMDs), include cardiac pacemakers, cardioverter/defibrillators, cardiomyostimulators, cardiac event monitors, various physiological stimulators including nerve, muscle, and deep brain stimulators, various types of physiological monitors and sensors, and drug delivery systems, just to name a few. IMDs typically include functional components contained within a hermetically sealed enclosure or housing, which is sometimes referred to as a “can.” In some IMDs, a connector header or connector block is attached to the housing, and the connector block facilitates interconnection with one or more elongated electrical medical leads. The header block is typically molded from a relatively hard, dielectric, non-conductive polymer. The header block includes a mounting surface that conforms to, and is mechanically affixed against, a mating sidewall surface of the housing.
It has become common to provide a communication link between the electronic circuitry hermetically sealed within the can of the IMD and an external programmer, monitor, or other external medical device (“EMD”) in order to provide for downlink telemetry transmission of commands from the EMD to the IMD and to allow for uplink telemetry transmission of stored information and/or sensed physiological parameters from the IMD to the EMD. Conventionally, the communication link between the IMD and the EMD is realized by encoded radio frequency (“RF”) transmissions between an IMD telemetry antenna and transceiver and an EMD telemetry antenna and transceiver. Generally, the IMD antenna is disposed within the hermetically sealed housing. However, the typically conductive housing can limit the radiation efficiency of the IMD RF telemetry antenna, thereby traditionally limiting the data transfer distance between the programmer head and the IMD RF telemetry antennas to a few inches. This type of system may be referred to as a “near field” telemetry system. In order to provide for “far field” telemetry, or telemetry over distances of a few to many meters from an IMD or even greater distances, attempts have been made to provide antennas outside of the hermetically sealed housing and within the header block. Many of such attempts of positioning an RF telemetry antenna outside of the hermetically sealed housing and in the header block have utilized wire antennas or planar, serpentine antennas, such as the antennas described in U.S. Pat. No. 7,317,946, which is hereby incorporated by reference in its entirety. However, the positioning of the antenna in the header block outside of the can has conventionally required the antenna to be connected to RF telemetry circuitry contained within the IMD through electrical feedthroughs that extend through the hermetically sealed can. Given the frequency, nature, and characteristics of the RF telemetry signals that are required to be transmitted from the antenna to the telemetry circuitry, the electrical feedthrough path for such telemetry signals can not typically be filtered, thereby leaving an open pathway for electromagnetic interference (EMI) signals or other types of interference signals to travel into the hermetically sealed can and negatively impact the circuitry contained within the IMD.